MOLECULAR PATHOGENESIS OF CANCER OF MUTATOR PHENOTYPE

微卫星突变子表型(MMP型)的胃肠癌与无MMP型的肿瘤在基因和表型上存在差异。APC、P53和K-ras癌基因在MMP型肿瘤中常见突变，而TGFbetaRII和Bax的突变失活基本上仅限于MMP型肿瘤。我们认为，作为遗传性非息肉病性结直肠癌(HNPCC)综合征和约15%的散发性胃肠道肿瘤的特征，肿瘤中是否存在并具有独特的基质金属蛋白酶途径，最终取决于某些肿瘤基因中是否存在以基质金属蛋白酶为靶点的序列。在特定的目标1中，我们将检验存在一条依赖于基质金属蛋白酶的致癌途径的假设。我们建议研究有无基质金属蛋白酶的肿瘤之间的基因差异。我们将完成对结肠癌(1a)和结肠癌(1a)中APC抑制基因突变的筛查；确定在结肠癌、乳腺癌和前列腺癌(特别是同源盒基因家族)中观察到的广泛的体细胞性DNA甲基化变化是否也延伸到基质金属蛋白酶+和基质金属蛋白酶-胃肠道肿瘤之间的基因型差异(1c)；并利用基质金属蛋白酶癌症的特殊表型特征来开发对基质金属蛋白酶(1c)的遗传性和散发性癌症的诊断方法。在特定的目标2中，我们将检验这一假设，即基质金属蛋白酶是通过多个突变体基因的突变失活而逐渐展开的。我们建议研究“突变另一个突变子的突变子”模型。我们将完成对结直肠癌和胃腺癌中DNA错配修复(MMR)基因家族(2a)已知成员的突变的筛查；对单个MMR突变基因及其组合在肿瘤细胞突变谱中的影响进行功能分析(2b)；并建立这些发现对MMP癌(2c)的预后价值。在特定的目标3中，我们将检验这一假设，即逃脱细胞凋亡是基质金属蛋白酶肿瘤发生的关键事件。我们建议研究Bax突变失活有助于基质金属蛋白酶肿瘤细胞逃避凋亡和肿瘤发生的机制。我们将完成对基质金属蛋白酶+和基质金属蛋白酶-肿瘤的Bax(3a)突变的筛查；通过体内和体外试验(3b)对Bax基因失活在基质金属蛋白酶癌中的作用进行功能分析；并探讨Bax体细胞突变失活对基质金属蛋白酶癌的预后价值。

Gastrointestinal cancers of the microsatellite mutator phenotype (MMP) differ in genotype and phenotype from tumors without the MMP. APC, p53 and K-ras cancer genes are commonly mutated in MMP- tumors while mutational inactivation of TGFbetaRII and BAX is essentially restricted to MMP+ cancers. We propose that the existence and distinctive features of the MMP pathway for cancer, characteristic of tumors of the Hereditary Non-Polyposis Colorectal Cancer (HNPCC) syndrome and about 15% of sporadic gastrointestinal cancers, ultimately depends on the presence in some cancer genes of sequences target for the MMP. In specific aim 1 we will test the hypothesis of the existence of a MMP-dependent pathway for cancer. We propose to investigate the differences in genotype between tumors with or without the MMP. We will complete the screening of mutations in the APC suppressor gene in MMP+ and MMP- colon tumors (1a); determine whether the differences in genotype between MMP+ and MMP- gastrointestinal tumors also extend to widespread somatic changes in DNA methylation that we have observed in colon, breast and prostate cancer, specifically in the homeobox gene family (1b); and exploit the peculiar phenotypic features of MMP cancer to develop diagnostic assays for hereditary and sporadic cancer of the MMP (1c). In specific aim 2 we will test the hypothesis that the MMP unfolds gradually by the mutational inactivation of multiple mutator genes. We propose to investigate the model of the "mutator that mutates another mutator". We will complete the screening of colorectal and gastric MMP+ adenocarcinomas for mutations in the known members of the DNA mismatch repair (MMR) gene family (2a); perform a functional analysis of the effect of mutations in individual MMR mutator genes and their combinations in the spectra of mutations in the tumor cells (2b); and establish the prognostic value of these findings for cancer of the MMP (2c). In specific aim 3 we will test the hypothesis that the escape from apoptosis is a critical event in tumorigenesis of the MMP. We propose to investigate the mechanisms by which BAX mutational inactivation contributes to the escape from apoptosis and to tumorigenesis of tumors cells of the MMP. We will complete the screening of MMP+ and MMP- tumors for mutations in BAX (3a); perform a functional analysis of the role of BAX gene inactivation in cancer of the MMP by in vivo and in vitro assays (3b); and investigate the prognostic value of BAX somatic mutational inactivation for cancer of the MMP.